1. Field of the Invention
The present invention relates in general to controlled release devices which are useful for dispensing an active compound from an article to the environment surrounding the article. More particularly, the present invention is directed to vapor emitting devices which form a laminate and provide a continuous release of a vapor at a substantially constant release rate. The present invention also relates to liquid release devices which form a laminate and provide a continuous release of a liquid or a solid dissolved in a liquid at a substantially constant release rate. The invention also relates to methods of preparing the laminates.
2. Description of Related Art
Various devices and compositions designed to release vapors or liquids from a compound or combinations of compounds have been in wide use over the years. For example, air freshener devices which continuously release an aroma into the environment surrounding the device exist in several varied configurations. Such devices range from a simple cardboard or paper structure saturated with air freshener for use in a confined area to elaborate and decorative air fresheners with more complicated aroma release mechanisms.
Also available are air fresheners with a "designer" appearance which adhere to surfaces and contain an air freshener compound within the device. The aromatic air freshener vapors are then released into the surrounding environment for a sustained length of time. The design and construction of these air fresheners is such that they release the vapors from the air freshener compounds at a rapid rate when the device is first put into service. As a result, the release rate diminishes significantly after a relatively short period of time. This produces a vapor release time profile where a relatively large amount of the total available air freshener is released in the initial part of the release period and only a small amount released thereafter. In many cases the aroma is too heavy during the initial part of the intended release period and too little or negligible at the end of the release period. Ideally, the release of the air freshener should be constant during the life of the device.
Other similar vapor releasing devices are perfume patches or pads which provide a temporary short term pleasant odor to the environment in the immediate vicinity of the patch or pad. The most prevalent use for these devices is to advertise perfumes to the public dispensing scent samples in the form of perfume patches or pads. The samples customarily consist of the perfume absorbed on a paper type support. They provide a short term release of the perfume's vapors after which the patch or pad is discarded.
U.S. Pat. No. 4,880,690 describes a perfume patch which is a laminate of polyurethane in combination with other layers including an impermeable backing and adhesive layer. The patch incorporates a perfume in the polyurethane layer and is intended to be adhered to the user's skin in areas such as behind the ear. Additionally, the patch may have an added pigment or decorative design on the polyurethane layer which lends some artistic appeal to the laminate.
The above described perfume pads and perfume patches have the same disadvantages as the air freshener release devices. The perfumes have a rapid rate of release during the initial phase of their life and a significantly reduced rate of release in the later stages. In order to prolong the use time of the patches and increase the release rate later in the life of the pad or patch, it is necessary to increase the perfume loading in the device. Increasing the loading of perfume in the device causes an increase in the initial release rate which in turn may cause an unpleasantly high amount of perfume vapor in the environment.
Controlled release devices also find application for the sustained release of breath fresheners. The use of water soluble mints and other suitable agents for controlling breath odor in devices designed to be contained or adhered to portions of the mouth are known in the art. These sustained release devices normally incorporate the active breath freshener in a device which slowly dissolves over a 1 to 4 hour period and releases the freshener as the dissolution proceeds. Breath fresheners which release active compounds in this manner have a relatively high surface area during the initial portion of the release period resulting in a high dose of the active compound. As dissolution of the article continues the surface area substantially decreases and the dose of the breath freshener necessarily decreases as well. This results in a less than desirable amount of freshener in the mouth.
Controlled release devices are used extensively in the pharmaceutical industry to provide therapeutic and diagnostic compounds to patients over periods of time ranging from minutes to days. In particular, skin patches have been used successfully in administering medications transdermally for several hours at a time with just one patch application. In particular, a patch described in U.S. Pat. No. 4,031,894 for delivering the sea sickness medication, scopolamine, is a five layer laminate designed to be attached to the skin behind the user's ear and deliver the drug through the patch's adhesive layer and into the user's circulatory system.
The utility of these skin patches, however, is limited to delivering therapeutic agents or other active compounds through the user's skin. The effectiveness of these skin delivery systems depends significantly upon the skin mass transport properties of the therapeutic agent and can vary from user to user. Additionally, these therapeutic agents frequently require a carrier or solvent to enhance their transport properties.
In addition to the above mentioned applications release devices have been used to release insect control and insect repellents on animals for decades. For example, flea and tick repellent and insecticides are incorporated in pet collars and then released onto the pet while the pet is wearing the collar to help control fleas and ticks which come into contact with the animal. Such collars are particularly adaptable for pets because it is difficult to apply insect repellents and insecticides to animal skin and fur on a regular basis.
Additionally, people have used insect repellents directly on the skin for over 30 years. Moreover, the use of insect repellents has increased dramatically in recent years in conjunction with the heightened concern associated with Lyme disease and the fear that mosquitos and other insects may contribute to the spread of AIDS. Known methods for delivering insect repellents in a manner which is safe and efficacious tend to be dangerous, short-acting and inconvenient. Recent clinical observations have shown that DEET, a leading topically applied insect repellent can cause severe central nervous system toxicity and even death from skin penetration. This is a particularly significant problem for children who have larger body surface area-to-mass ratios and higher skin permeability. Additionally, children tend to lick their fingers and hands, which can cause them to ingest the insect repellents.
Another problem associated with topically applying insect repellents directly to the skin is that they are effective for only short periods of time. Because the insect repellent is removed by skin absorption, evaporation, perspiration, and through participation in water activities, it must be reapplied at frequent intervals. The requirement for frequent reapplications results in a continual threat of systemic toxicity to the user.
There is a need to provide a controlled release device which will continuously release vapor into the environment surrounding the user at a controlled, and substantially constant rate over the intended life of the controlled release article.
There is additionally a need to provide controlled release devices which safely and effectively deliver active compounds and therapeutic agents without applying the active compound directly to the skin or depending upon the mass transport properties of the active compound through the skin.
There is also a need to provide a liquid releasing device which will continuously release liquids into a suitable environment at a controlled and substantially constant rate over the intended life of the release article.